[[cat-shards]] == cat shards The `shards` command is the detailed view of what nodes contain which shards. It will tell you if it's a primary or replica, the number of docs, the bytes it takes on disk, and the node where it's located. Here we see a single index, with one primary shard and no replicas: [source,js] --------------------------------------------------------------------------- GET _cat/shards --------------------------------------------------------------------------- // CONSOLE // TEST[setup:twitter] This will return [source,txt] --------------------------------------------------------------------------- twitter 0 p STARTED 3014 31.1mb 192.168.56.10 H5dfFeA --------------------------------------------------------------------------- // TESTRESPONSE[s/3014/\\d+/] // TESTRESPONSE[s/31.1mb/\\d+(\.\\d+)?[kmg]?b/] // TESTRESPONSE[s/192.168.56.10/.*/] // TESTRESPONSE[s/H5dfFeA/node-0/ non_json] [float] [[index-pattern]] === Index pattern If you have many shards, you may wish to limit which indices show up in the output. You can always do this with `grep`, but you can save some bandwidth by supplying an index pattern to the end. [source,js] --------------------------------------------------------------------------- GET _cat/shards/twitt* --------------------------------------------------------------------------- // CONSOLE // TEST[setup:twitter] Which will return the following [source,txt] --------------------------------------------------------------------------- twitter 0 p STARTED 3014 31.1mb 192.168.56.10 H5dfFeA --------------------------------------------------------------------------- // TESTRESPONSE[s/3014/\\d+/] // TESTRESPONSE[s/31.1mb/\\d+(\.\\d+)?[kmg]?b/] // TESTRESPONSE[s/192.168.56.10/.*/] // TESTRESPONSE[s/H5dfFeA/node-0/ non_json] [float] [[relocation]] === Relocation Let's say you've checked your health and you see relocating shards. Where are they from and where are they going? [source,js] --------------------------------------------------------------------------- GET _cat/shards --------------------------------------------------------------------------- // CONSOLE // TEST[skip:for now, relocation cannot be recreated] A relocating shard will be shown as follows [source,txt] --------------------------------------------------------------------------- twitter 0 p RELOCATING 3014 31.1mb 192.168.56.10 H5dfFeA -> -> 192.168.56.30 bGG90GE --------------------------------------------------------------------------- // TESTRESPONSE[non_json] [float] [[states]] === Shard states Before a shard can be used, it goes through an `INITIALIZING` state. `shards` can show you which ones. [source,js] --------------------------------------------------------------------------- GET _cat/shards --------------------------------------------------------------------------- // CONSOLE // TEST[skip:there is no guarantee to test for shards in initializing state] You can get the initializing state in the response like this [source,txt] --------------------------------------------------------------------------- twitter 0 p STARTED 3014 31.1mb 192.168.56.10 H5dfFeA twitter 0 r INITIALIZING 0 14.3mb 192.168.56.30 bGG90GE --------------------------------------------------------------------------- // TESTRESPONSE[non_json] If a shard cannot be assigned, for example you've overallocated the number of replicas for the number of nodes in the cluster, the shard will remain `UNASSIGNED` with the <> `ALLOCATION_FAILED`. You can use the shards API to find out that reason. [source,js] --------------------------------------------------------------------------- GET _cat/shards?h=index,shard,prirep,state,unassigned.reason --------------------------------------------------------------------------- // CONSOLE // TEST[skip:for now] The reason for an unassigned shard will be listed as the last field [source,txt] --------------------------------------------------------------------------- twitter 0 p STARTED 3014 31.1mb 192.168.56.10 H5dfFeA twitter 0 r STARTED 3014 31.1mb 192.168.56.30 bGG90GE twitter 0 r STARTED 3014 31.1mb 192.168.56.20 I8hydUG twitter 0 r UNASSIGNED ALLOCATION_FAILED --------------------------------------------------------------------------- // TESTRESPONSE[non_json] [float] [[reason-unassigned]] === Reasons for unassigned shard These are the possible reasons for a shard to be in a unassigned state: [horizontal] `INDEX_CREATED`:: Unassigned as a result of an API creation of an index. `CLUSTER_RECOVERED`:: Unassigned as a result of a full cluster recovery. `INDEX_REOPENED`:: Unassigned as a result of opening a closed index. `DANGLING_INDEX_IMPORTED`:: Unassigned as a result of importing a dangling index. `NEW_INDEX_RESTORED`:: Unassigned as a result of restoring into a new index. `EXISTING_INDEX_RESTORED`:: Unassigned as a result of restoring into a closed index. `REPLICA_ADDED`:: Unassigned as a result of explicit addition of a replica. `ALLOCATION_FAILED`:: Unassigned as a result of a failed allocation of the shard. `NODE_LEFT`:: Unassigned as a result of the node hosting it leaving the cluster. `REROUTE_CANCELLED`:: Unassigned as a result of explicit cancel reroute command. `REINITIALIZED`:: When a shard moves from started back to initializing, for example, with shadow replicas. `REALLOCATED_REPLICA`:: A better replica location is identified and causes the existing replica allocation to be cancelled.